1. Field of the Invention
Biocatalytic processes have become very important for the chemical industry. In this connection, carrying out chemical reactions with the aid of biological catalysts is particularly interesting in those fields of application in which it is possible to utilize the frequently found enzyme property of preferably converting or forming in chemical reactions with chiral or prochiral components one of the two enantiomers.
Essential requirements for utilizing said advantageous properties of enzymes are the availability of said enzymes in industrially required amounts and a sufficiently high reactivity and also stability under the real conditions of an industrial process.
2. Description of the Related Art
Cyanohydrins are a particularly interesting class of chiral chemical compounds. Cyanohydrins are important, for example, in the synthesis of α-hydroxy acids, α-hydroxyketones, β-aminoalcohols which are used for producing biologically active substances, for example pharmaceutical active substances, vitamins or pyrethroid compounds.
Said cyanohydrins are prepared by addition of hydrocyanic acid to the carbonyl group of a ketone or aldehyde.
Industrial production of chiral compounds such as, for example, (S)-cyanohydrins was made possible by making use of the enzyme (S)-hydroxynitrile lyase from Hevea brasiliensis and is described, for example, in WO 97/03204, EP 0 951561 and EP 0 927 766.
However, there is a large variety of interesting chemical compounds for which the R enantiomers are important for industrial applications. Up until now, only processes which can be used only on the laboratory scale have been described for preparing a number of products (e.g.: EP 0 276 375, EP 0 326 063, EP 0 547 655). In this connection, mainly enzyme preparations obtained from plants of the Rosaceae family, for example from the kernels of almonds (Prunus amygdalus), were used.
Recently, Prunus species have become more and more important so that attempts were made to investigate said species in greater detail.
The specialist literature, for example Plant Physiology, April 1999, Vol 119, pp. 1535–1546, discloses that Prunus species can contain a plurality of R-HNL isoenzymes. These isoenzymes are expressed at different levels in various tissues of the plant. It was possible to identify in the plant Prunus serotina which is a close relative of Prunus amygdalus 5 different isoenzymes up until now and to sequence their genes. Only one Prunus amygdalus isoenzyme has been described up until now in Planta (1998) 206: 388–393, and this isoenzyme is most strongly expressed in the flower bud. A gene for said R-HNL isoenzyme has already been isolated and the cDNA has been sequenced.
However, no successful (functional) heterologous expression of such a gene has been reported in the specialist literature or patent literature.
Industrial applications on a large scale, too, have not been carried out up until now, the main reason being that enzyme preparations from almond kernels with hydroxynitrile lyase activity have not been available up until now in sufficient quantities and at justifiable costs.